The YF-17D Yellow Fever vaccine has attracted considerable interest in recent years as a model of acute viral infection in humans. Immunization with YF-17D leads to transient viremia and subsequently to potent activation of both the innate and adaptive immune systems. Clearance of the virus is thought to be attributable to a robust CD8+ T-cell response that is characterized by a rapid expansion of a diverse population of virus-specific effector CD8+ cells. This expansion peaks at day 14 post immunization, by which time viremia is no longer detectable, and thereafter contracts rapidly to leave a population of long-lived memory CD8+ T cells, which comprise ~1% of the peripheral blood CD8+ T cells at day 30. Thus, the CD8+ T cell response to YF-17D represents an ideal model system in which to define the natural history, clonal composition, and population dynamics of an effective acute antiviral T cell response. We have developed a suite of molecular and computational procedures for defining, with unprecedented resolution and precision, the number of distinct antigen receptors and the frequency of cells with each receptor, in any defined population of lymphocytes. Using these procedures, which are based on high-throughput, single molecule DNA sequencing, we have recently profiled a significant fraction of the entire naive and memory CD8+ T cell repertoires of two healthy adults. In this application, we propose to use these methods to study the CD8+ T cell response in healthy adults who receive the YF-17D vaccine. We will define both the population of CD8+ cells that are activated by YF-17D immunization and comprise the effector response at day 14, as well as the population of cells that contribute to long-term virus-specific memory. Comparison of the effector and memory virus-specific repertoires with each other, and with the repertoire prior to immunization, will provide valuable insights into the CD8+ T cell response to an acute viral infection, and will provide the foundation on which to evaluate novel vaccines in the future. PUBLIC HEALTH RELEVANCE: We propose to study the cellular immune response to an acute viral infection using the yellow fever vaccine as a model. A key component of our study is the development of a novel high- throughput sequencing technology to measure and track millions of T cells in parallel.